(1) Field of the Invention
The invention relates to an electroless gold plating solution, and more particularly an alkaline electroless gold plating solution.
(2) Description of the Prior Art
A conventional alkaline electroless gold plating solution is applied in such a state as to raise an alkalinity by adding herein a pit adjustor such as potassium hydroxide. However, an excessively high alkalinity will undesirably accelerate the decomposition of the solution, although it increases the deposition rate of gold. Thus, a technique for eliminating such inconvenience described above has been disclosed in Japanese Laid-open Patent Publication No. Sho 62-99477 which uses amines such as triethanolamine to attain a desired alkalinity in addition to a pH adjustor such as potassium hydride.
A problem about triethanolamine is that it is strongly adsorbed to the plating site, which causes unwanted deposition of gold. For example, in an attempt to deposit gold onto metallized parts only on the surface of a workpiece, small amount of gold may deposit outside those areas. This may result in undesired electrical continuity between separate plated parts arranged at a short distance.
The present invention aims at elimination of such problems associated with conventional plating solutions, and provides an electroless gold plating solution from which gold deposits exactly onto desired parts of the workpiece without undesirable spread of the plated area.